BeneficialSpongy moth

Bt for spongy moth (gypsy moth)

Bacillus thuringiensis kurstaki · microbial insecticide
Against spongy moth

Btk works well only on young caterpillars, and on large trees it needs a licensed applicator with the right equipment. UMass Extension's test is the head: all-black heads mean the spray will work, and yellow markings mean it is late. About 90% of the feeding happens in the last two instars, so a spray in late June mostly misses. Cover the foliage thoroughly, and let the fungus Entomophaga maimaiga do the rest in a wet spring.

RateLabel rate — 4 tsp per gallon of water (Thuricide and Monterey B.t. shade-tree directions, which list it as gypsy moth)
TimingFrom egg hatch (usually the first week of May in Massachusetts), once the caterpillars have settled to feed and while caterpillars have all-black heads and are under about ¾ inch; Thuricide says spray at the 2nd–3rd instar and repeat in two weeks

Before you order

A bacterium sprayed on leaves. Caterpillars that eat it stop feeding and die within a few days. It works only on the larvae of moths and butterflies, and has little or no effect on bees, lady beetles, lacewings or parasitic wasps. How it works, how to tell it has established and the supplier list are on the full Bacillus thuringiensis kurstaki profile.

Other controls for spongy moth

No other reviewed control is listed for this pest yet.